add twitch API stuff, add follow/sub/cheer labels

twitch/public/labels.css

@@ -0,0 +1,10 @@
+body {
+    margin: 0;
+}
+
+#label {
+    margin: 16px;
+    font-family: "Inter", sans-serif;
+    font-size: 64px;
+    font-weight: bold;
+}

twitch/public/labels.js

@@ -0,0 +1,60 @@
+const labelEl = document.getElementById("label");
+
+const selectedLabel = new URLSearchParams(location.search).get("l");
+const labelLatestFollower   = "latest-follower"
+const labelLatestSubscriber = "latest-subscriber"
+const labelLatestCheer      = "latest-cheer"
+const allowedLabels = [
+    labelLatestFollower,
+    labelLatestSubscriber,
+    labelLatestCheer,
+]
+
+/**
+ * @param {string} selectedLabel
+ */
+async function sync() {
+    if (selectedLabel == null) {
+        const exampleUrl = 
+            location.pathname +
+            "?l=" +
+            labelLatestFollower;
+
+        labelEl.innerHTML =
+            "Needs label to listen to, " +
+            `such as <a href="${exampleUrl}">${labelLatestFollower}</a>`;
+        console.error("Needs label to listen to, such as " + exampleUrl);
+        return;
+    }
+
+    let eventSource;
+    try {
+        eventSource = new EventSource("/twitch/sse?l=" + selectedLabel);
+    } catch (err) {
+        console.error("Failed to connect to event source", err);
+        return;
+    }
+
+    eventSource.addEventListener("error", () => {
+        eventSource.close();
+        console.error("Connection lost, or an error has occurred.");
+        console.log("Attempting to reconnect...");
+
+        // TODO: stop reconnecting after 10 failed attempts
+
+        setTimeout(() => {
+            sync();
+        }, 1000);
+    });
+
+    eventSource.addEventListener("update", event => {
+        console.log(event.data);
+        labelEl.innerText = event.data;
+    });
+
+    eventSource.addEventListener("open", () => {
+        console.log("Connected.");
+    });
+}
+
+sync();